The risk of a blood clot caused by hormonal contraceptives falls rapidly once it is no longer used, new research indicates, with most of this fall happening within two to four weeks.
It has long been known that combined hormonal contraceptives – including contraceptive pills, vaginal rings and transcutaneous patches – can elevate the risk of blood clots by about three-fold.
What has not been clear is how long it takes for risk to fall back to baseline levels once contraceptives are ceased. This has led to a lack of clarity in guidelines for when people should stop taking combined hormonal contraceptives before surgery or planned periods of immobility.
Study leader Dr Marc Blondon, of the University Hospitals of Geneva in Switzerland, said: “Our goal was not to look at the thrombotic risk of contraceptives, but to determine how long that risk takes to normalise after stopping contraceptives.”
The study included 66 women who were stopping combined hormonal contraceptives, and 28 women not using the products. Blood samples were taken at six timepoints (three for the control group), and clotting biomarkers were measured as a proxy for clotting risk.
Elevated levels of clotting markers were seen in women using the contraceptives, but this “dropped precipitously” within one to two weeks after they stopped using them, say the researchers.
After 12 weeks the levels of all biomarkers were comparable to the control group. The researchers say that most of the elevated risk had disappeared within two to four weeks after contraceptive use stopped. The results were published in the journal Blood.
Dr Blondon commented: “It’s reassuring to know that the possible harm of the pill goes away rapidly when one stops taking it.
“These findings can help to inform discussions around whether combined hormonal contraceptives are right for the patient, as well as patient-surgeon discussion of whether the benefit of stopping for a short time actually exceeds the risks.
“It’s very important to talk about the benefits of contraception because it’s crucial to avoid unwanted pregnancy and for women to have the choice of a planned pregnancy.”
Hugon-Rodin J, Fontana P, Poncet A, Streuli I, Casini A, Blondon M. (2024) “Longitudinal profile of estrogen-related thrombotic biomarkers after cessation of combined hormonal contraceptives.” Blood, doi: 10.1182/blood.2023021717.
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